Traps, Rogues, and Searching every *&%$&* 5' square in the entier friggin' dungeon.
Veteran gamers usually realize that a trap laden dungeon can cause an adventure to come crashing to a snail's pace, as the Rouge has to roll a Search check for every 5 (or is it 10) ft square the party wants to traverse.
In my games, (once the party suspects traps) the rogue is passively making Search checks as he goes along. I only have him roll when he the sucess/failure matters (ie trap present) of when they encounter a distinctive feature (Statue, Tiled floor, etc). This speeds things up.
In your case. they should have figured out what was going on after the 2nd trap (Fool me once, shame on you, fool me twice....) However, as a DM you should have said something to the effect, "So after bob's encounter with those Evan's Grasping Invasive Tentacles (Thanks OotS), what precautions are you taking?"
This is the party's time to say things like "I cast Detect Traps". "I drink my Potion of Spell Resistance" "I start looking for traps".
I mean, really, at some point, the rogue should have told you he was searching as he went along (not just for traps, but hidden foes, false doors, etc).
From what I can tell, this seems to be a case of both sides assuming the other Knew what the other was talking about, and coming to completly different conclusions.
In other words, it takes 2 to miscommunicate.
Tell him you're sorry, but WE just didn't communicate effectively, what can WE do to make sure it doesn't happen again.